ipv6: make sure to initialize sockc.tsflags before first use

ipv6: make sure to initialize sockc.tsflags before first use

BugLink: http://bugs.launchpad.net/bugs/1677589
[ Upstream commit d515684d78148884d5fc425ba904c50f03844020 ]

In the case udp_sk(sk)->pending is AF_INET6, udpv6_sendmsg() would
jump to do_append_data, skipping the initialization of sockc.tsflags.
Fix the problem by moving sockc.tsflags initialization earlier.

The bug was detected with KMSAN.

Fixes: c14ac9451c34 ("sock: enable timestamping using control messages")
Signed-off-by: Alexander Potapenko <glider@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>